It was an emotional win for the fifth seed, who lost three straight finals earlier during the year.
"It is a little bit (of a relief)," Fish said. "If I had lost four finals this year, I probably would have started second-guessing myself."
The 19-year-old Soderling, cheered on by his home crowd, came back from a break down in the second set to level the match following some uninspiring play by the American.
"It felt like a Davis Cup match, but they also clapped for me," Fish said. "I love to play in that kind of atmosphere.
"I think I heard one or two people screaming 'Mardy'.
"I felt in control up to my 2-0 lead in the second set, I felt I was cruising and that it was probably going to be over in two sets.
"I couldn't tell what happened then. He handled my serve better than anyone else here, and I had only been broken once before during the entire tournament.
"I don't know if I was passive, I didn't lose games, it felt like he won them. He had me on my heels and he made me play one of my best matches this year."
PHENOMENAL SERVING
Fish tired in the deciding set but survived thanks to his phenomenal serve and 17 aces. Soderling contributed with some basic mistakes, wasting a 2-0 lead in the tie-break with a wide forehand.
"I did rely a lot on my serve. That's what I do when I play," Fish said.
Fish went 4-2 up with a cross-court forehand pass and then held his serve for 6-3. Soderling saved a match point before Fish clinched the tie-break 7-4.
"It feels a little bitter, having lost after coming this close," Soderling said. "But after some time...I think I will be content with this week."
The win put 21-year-old Fish, a childhood friend of Andy Roddick, into the top 20 of the ATP's entry rankings system for the first time of his career.
Fish, who next plays in Paris, said he was already working on his goals for next season. "Winning more tournaments, a Masters Series tournament and finishing in the top ten is what I'm looking at. I'm still pretty young for the game of tennis."
